Rare-earth ions doped into a suitable laser host, such as crystal (e.g. YAG), ceramic, or glass (silica), are used to form lasers and optical amplifiers used for a variety of applications such as materials processing, laser surgery, etc. High power lasers for these applications operate within the 1-2 μm spectral range.
Current laser materials used for mid-wave infrared (MWIR) and long-wave infrared (LWIR) solid-state lasers are hygroscopic or lack suitable sites for the active rare-earth-doping ion. Lasers based on these materials operate at low power levels and are not durable.
While direct mid-IR laser emission in halide materials such as LaCl3 and KPb2Cl5 has been demonstrated (S. R. Bowman, et al., “A 7-μm praseodymium-based solid-state laser,” IEEE J. Quantum Electron. 32(4):646-649 (1996); S. R. Bowman, et al., “New mid-IR laser based on an erbium activated low phonon energy crystal,” Conference on Lasers and Electro-Optics, J. Kafka et al., eds., OSA Technical Digest (Optical Society of America, 2001), paper CFD2; C. Nostrond, et al., “Room temperature laser action at 4.3-4.4 μm in CaGa2S4:Dy3+,” Opt. Lett. 24(17):1215-1217 (1999)), the halide host materials suffer from either durability issues due to high hygroscopicity (LaCl3) or low-rare-earth dopant concentration due to lack of a suitable site for rare-earth doping (KPbCl5, CaGa2S4). Lasers based on these materials operate at low power levels, and are not durable.
Mid-IR transitions have also been studied in glass hosts such as chalcogenide glass (L. B. Shaw, et al., “Mid-Wave IR and Long-Wave IR Laser Potential of Rare-Earth Doped Chalcogenide Glass Fiber,” IEEE J. Quantum Electron., 48(9):1127-1137 (2001)). Here again, the chalcogenide glasses do not possess a site for the rare-earth ion, making rare-earth doping difficult.
CaLa2S4 is an environmentally-durable cubic crystalline material with broad transmission out to 14 μm. CaLa2S4 has been fabricated and studied in the past as a potential long-wave-IR window and dome material (J. Corvino, et al., “Development of Calcium Lanthanum Sulfide as an 8-12 μm Transmitting Ceramic,” Proc. SPIE, Vol. 0505, Advances in Optical Materials, pages 42-46 (1984)); however, the potential of calcium lanthanum sulfide and other ternary sulfides as a host material for MWIR and LWIR lasers has not previously been assessed.